The invention relates to a medical fluid circuit and a control method of a medical fluid circuit.
Specifically, though not exclusively, the invention can be usefully applied in supplying a medical fluid, such as for example an infusion fluid or a dialysis fluid.
In particular, the medical fluid circuit of the invention comprises a source batch of the medical fluid which during use is emptied and has to be replaced by another, full source batch.
An infusion circuit is known which comprises an infusion pump that sources the infusion liquid from a batch container and sends it to an individual (directly into the body of the individual or via an extracorporeal blood circuit). Also known is using a monitoring system of the weight of the container used, for example a scales applied to the container. When the weight measured by the scales does not fall for a given period of time, the control unit of the infusion circuit signals that the container is empty and stops the infusion pump to prevent undesired air ingress into the infusion line.
There can however be a certain lapse of time after effective emptying of the container and the moment the infusion pump halts, during which time the infusion pump can draw air instead of infusion fluid into the infusion line. A certain quantity of air can therefore enter into an expansion chamber predisposed along the infusion line for degassing the infusion fluid via air-liquid separation. By effect of the introduction of air, the liquid level in the expansion/degassing chamber will diminish. When the operator intervenes to replace the empty container with another, full container, she or he normally controls that the liquid level in the expansion chamber is the desired level. If this is not the case, the operator adjusts the liquid level manually, for example by removing excess air from the expansion chamber by means of an aspirating syringe connectable to the expansion chamber.
A drawback of the prior art is the risk of having an excess of air in the infusion circuit on restarting the infusion fluid supply, after changing the batch container and following a missed control and intervention on the part of the operator.
The prior art comprises various medical fluid circuits which use a source batch of medical fluid.
WO 2005/065749 shows a system for detecting emptying of a container of an infusion fluid, in which an infusion line is provided with an expansion chamber in the form of a drip chamber, an infusion pump downstream of the expansion chamber and a pressure sensor between the expansion chamber and the infusion pump. The pressure sensor is used for recognising the emptying of the container.
U.S. Pat. No. 5,563,584 shows an infusion system with a monitoring device of the batch container level of an infusion liquid. The device comprises a pressure sensor arranged at the outlet of the container for receiving the pressure exerted by the liquid internally of the container. When the container is close to empty, the pressure drops below a certain threshold.
EP 1319417 shows an apparatus for monitoring a medical fluid system (for example an infusion or dialysis apparatus) in which a certain quantity of fluid is extracted from/injected into the system and the pressure difference in the system is measured before and after the extraction/injection. This difference is used to deduce some parameters which describe the situation of the system, such as for example the quantity of gas present in the system.
U.S. Pat. No. 6,855,122 shows an infusion system comprising a batch container of a substitution fluid, an expansion chamber in the form of a drip chamber, a pump and a fluid-empty sensor arranged between the container and the pump.